Project Summary: Found in nearly all aerobic organisms, oxygen-activating enzymes with non-heme iron centers are often employed to perform demanding transformations. The major aim of this research project is to gain insights into the nature of oxygen activation at iron enzymes through the synthesis and characterization of high-valent iron-oxo complexes that mimic the structure and reactivity of key catalytic intermediates. In particular, novel strategies will be employed to generate complexes that model the reactive species of soluble methane monooxygenase (MMO), an enzyme that uses oxygen to convert methane to methanol. By allowing certain bacteria to utilize methane as their sole source of carbon and energy, MMOs eliminate nearly a billion tons of this potent greenhouse gas from the atmosphere each year. Moreover, there is considerable interest in replicating the MMO reaction industrially in order to provide an environmentally-clean means of generating methanol, a chemical feedstock and potential energy source. Thus, the study of high-valent diiron species carries enormous biological, environmental, and technological implications. The crucial step in the sMMO catalytic cycle involves the oxidation of methane by a poorly- characterized diiron(IV)-oxo species known as intermediate Q. Building upon the recent success in generating mononuclear iron(IV)-oxo complexes, this proposal describes two original routes for the synthesis of small-molecule models of intermediate Q that reproduce its bis-oxo-diiron(IV) "diamond core". The resulting complexes will be characterized with a variety of spectroscopic and structural methods, such as electronic absorption, resonance Raman, Mossbauer and X-ray absorption spectroscopies, and their reactivites towards organic substrates will be examined. The results are expected to advance our current understanding of the geometric and electronic structures of intermediate Q, and provide new insights into mechanism of oxygen activation in biological systems. Additionally, this project may lead to the development of biomimetic catalysts for methane oxidation. Relevance: By synthesizing small-molecule iron complexes that replicate the structures and reactivities of important biological species, this research proposal aims to better understand those processes in humans and other organisms that require oxygen activation at iron centers in enzymes. Additionally, this project may lead to the development of new catalysts that will allow chemists to use oxygen to carry out environmentally- friendly transformations of hydrocarbons, thereby reducing pollution and levels of greenhouse gases in the atmosphere.